U.S. Pat. No. 5,789,646 discloses a process for the double bond isomerization of an olefin, which process comprises contacting a feed comprising the olefin with an isomerization catalyst which is a solid acid catalyst. The solid acid catalysts which feature in the working examples of U.S. Pat. No. 5,789,646 are an H-ZSM-5 having a silicon/aluminum atomic ratio of 25 and a crosslinked sulfonic acid ion exchange resin. U.S. Pat. No. 5,789,646 teaches that the feed comprising the olefin should preferably be dry.
U.S. Pat. No. 4,697,040 discloses a process for the double bond isomerization of an olefin, which process comprises contacting a feed comprising the olefin with an isomerization catalyst which comprises a zeolite in the sodium form. The zeolite catalyst of U.S. Pat. No. 4,697,040 is a specific Y type zeolite, designated LZ-Y52 (trademark). In the prior art discussion of U.S. Pat. No. 4,697,040, referring to U.S. Pat. No. 3,686,250, it is taught that highly acid isomerization catalysts have the disadvantage that they are deactivated at an undesirably high rate by traces of impurities so that isomerization catalysts of moderate acidity are generally preferred from a long term activity cost of view and from a low cost viewpoint. U.S. Pat. No. 3,686,250 suggests employing a guard bed technique of a catalyst charge of a previous run placed in the flow path ahead of the principle catalyst bed.
U.S. Pat. No. 4,749,819 discloses a process for the double bond isomerization of an olefin, which process comprises contacting a feed comprising the olefin with an isomerization catalyst which comprises a zeolite of a suitable channel size, preferably a ferrierite. U.S. Pat. No. 4,749,819 teaches that the feed may be pretreated by contacting with a refractory inorganic oxide, for example alumina, silica, zirconia, magnesia, silica-alumina, silica-alumina-chromium, etc., or another, unspecified type of molecular sieve.
U.S. Pat. No. 5,237,120 discloses a process for the double bond isomerization of an olefin, which process comprises contacting a feed comprising the olefin with an isomerization catalyst which comprises a zeolite of which the outer surface has at least partially been deactivated for acid catalysed reactions. In the working examples of U.S. Pat. No. 5,237,120 the feed is pretreated by contacting it with a pretreating material consisting of γ-alumina, reduced copper chromite and molecular sieve zeolite-3A. Zeolite-3A has a pore size of 0.3 nm.
Although much attention has been given to the pretreating of the feed to an olefin double bond isomerization process, it is still desirable to improve the pretreatment thereby improving the performance of the isomerization catalyst.